The goal of this PPG is to identify mechanisms underlying the molecular triggers for fatal cardiac arrhythmias. The central hypothesis of the PPG is that adrenergic mediated perturbations of calcium (Ca) homeostasis, contribute to triggers that initiated fatal cardiac arrhythmias. We propose that polymorphisms that alter beta adrenic receptor (betaAR) function (Project 1, J. Russo) are associated with increased risk of SCD. Ion channel mutations can cause action potential duration (APD) prolongation (Project 3, R.S. Kass) that promotes sarcoplasmic reticulum (SR) Ca overload and contributes to alterations in local and global Ca signals in cardiomyocytes (Project 4, W.J. Lederer), exacerbated by adrenergic stimulation. Genetic forms of human SCD, Long Q-T Syndrome (LQTS), and Brugada Syndrome (BrS) serve as models to identify mechanisms that trigger fatal cardiac arrhythmias. The hypothesis to be tested in this Project (Project 2) is that adrenergic mediated phosphorylation of the intracellular Ca release channel/ryanodine receptor (RyR2) increases channel open probability (Po) and contributes to pathologic SR Ca release that can trigger ventricular arrhythmias Preliminary data show that: 1) adrenergic stimulation causes PKA hyperphosphorylation of RyR2 on serine hyperphosphorylation dissociates FKBP12.6 from the channel and increases the RyR2 PO. Aim 1 is to characterize PKA phosphorylation dissociates FKBP12.6 from the channel and increases the RyR2 Po. Aim 1 is to characterize PKA phosphorylation of RhR2 using mutant (PKA phosphorylation deficient) RyR2 S2809A and "constitutively PKA phosphorylated" RyR2 S2809D. The hypothesis to be tested is that adrenergic mediated hyperphosphorylation of S28098 in RyR2 channels can alter single channel properties leading to defective Ca homeostasis. Aim 2 is to determine the mechanism whereby PKA phosphorylation activities dependence for activation and inhibition of the channel. The hypothesis to be tested is that PKA dependent is to determine the effects of variant betaARs on RhR2 function. Variant betaARs, identified in Project 1, will be co-expressed with RyR2 to determine the effects of altered adrenergic signaling on SR calcium release channel function. The hypothesis to be tested si that variant betaARs, found in individuals at high risk for SCD, modulate RyR2 function resulting in defective Ca homeostasis.